1. Technical Field
The present disclosure relates to macrocycle structures having triazole-carbazole units configured to bind large anions.
2. Description of Related Art
Considerable interest exists for removing hazardous chemical ions from the environment, such as large anions. Large anions are hard to bind and present significant environmental hazards. Few examples of charge-neutral chelators exist that can bind larger anions like these with such high affinities. For example, perchlorate (ClO4−) is a large anion by-product of munitions and jet propulsion that is an acute environmental hazard as it accumulates in waterways such as the Colorado River. Perchlorate presents a human health risk as it interferes with thyroid hormone biosynthesis and thus impacts how energy is managed in the body. Current approaches to removing ClO4− make use of ion-exchange resins, either single-use or recyclable, and each has its pros and cons. But, they share issues with the level of ClO4− that can be removed (the actual value of the cleaned water efflux from the ion-exchange beds is sometimes below the limit of detection). There is a need for new reagents to allow detection and removal of ClO4− to lower levels in efflux water.
In certain research and industrial applications with ion-exchange processes, the unwanted removal of sulfate that competes with adsorption sites to lower the ClO4− capacity of the ion-exchange resin. Furthermore, those exchange resins rely upon cationic sites for exchanging anions for ClO4−. Thus, it has not been possible to use neutral organic molecule receptors that are capable of chelating anions like ClO4−. Such organic molecule receptors that are specifically designed for large anions like ClO4− have not been targeted. This situation is likely a result of the long-accepted idea that such anions are only weakly coordinating (M. R. Rosenthal, J. Chem. Ed. 1973, 50, 331-335). Thus, there is a need for new compounds with a variety of chemical sequences to exquisitely tune the properties or usage for binding large anions like ClO4− Furthermore, most anion-capture receptors are molecules that do not organize into thin films, which might offer certain advantages as an absorbant or sensory material.
Shape persistent macrocycles are attractive multifunctional molecules bearing inner cavities to bind guests (such as the aforementioned large anions) and outer surfaces to direct hierarchical self-assembly. While guest recognition has a rich history, the assembly of macrocycles and the supramolecular information that needs to be encoded into their surfaces to direct their self-organization is of ongoing interest. Examples include liquid-crystalline ordering of crown ethers for ion conduction (T. Kato, N. Mizoshita, K. Kishimoto, Angew. Chem. Int. Ed. 2006, 45, 38-68), pore-forming stacks of amido macrocycles for ion transport across membranes (A. J. Helsel, A. L. Brown, K. Yamato, W. Feng, L. Yuan, A. J. Clements, S. V. Harding, G. Szabo, Z. Shao, B. Gong, J. Am. Chem. Soc. 2008, 130, 15784-15785), and organized nanostructures for organic electronics (D. Adam, P. Schuhmacher, J. Simmerer, L. Haussling, K. Siemensmeyer, K. H. Etzbachi, H. Ringsdorf, D. Haarer, Nature 1994, 371, 141-143; A. A. Gorodetsky, C.-Y. Chiu, T. Schiros, M. Palma, M. Cox, Z. Jia, W. Sattler, I. Kymissis, M. Steigerwald, C. Nuckolls, Angew. Chem. Int. Ed. 2010, 49, 7909-7912). The informed design of macrocycles therefore requires parallel consideration of multiple design criteria. These designs also benefit from building blocks that can aid macrocycle synthesis (W. Zhang, J. S. Moore, Angew. Chem. Int. Ed. 2006, 45, 4416-4439).